The invention relates to a circuit arrangement for a picture reproducing apparatus comprising an amplitude limiter having an input and an output, which amplitude limiter is constructed to change the polarity of its output signal when a frequency-modulated picture signal on its input passes a threshold value, and a frequency demodulator, which is coupled to the output of the amplitude limiter.
A picture reproducing apparatus is to be understood to mean an apparatus which reproduces signals recorded on, for example, a magnetic tape or an optical storage disk and converts them into signals which can be processed by, for example, a television receiver. Such a picture reproducing apparatus may be a video recorder or a video-disk player. A circuit arrangement as defined in the foregoing for a video recorder is known from the magazine "Funkschau", 1984, Volume 15, pages 42 to 45, in particular FIG. 5. This circuit arrangement processes a frequency-modulated luminance signal (picture signal) which is applied from the magnetic tape to an amplitude limiter via video heads, a head amplifier and two series-connected filters. The amplitude limiter amplifies and limits the signal in such a way that when a constant threshold value is exceeded the polarity of the output signal of the amplitude limiter changes. The output signals of the amplitude limiter are applied to a frequency demodulator, which supplies a demodulated picture signal.
In the case of such a frequency-modulated luminance signal the upper limit value of frequency swing of the carrier-modulated wave corresponds to a white picture content and the lower limit value to a black picture content. If the picture content of the recorded frequency-modulated luminance signal suddenly changes from a black to white, i.e. the frequency of the frequency-modulated luminance signal jumps from a lower to a high frequency, the amplitude during reproduction via the tape-to-video head transmission path and the filters will decrease substantially. In the case of an unfavorable phase relationship of the signal it may happen that one or more cycles of the frequency-modulated signal do not intersect the threshold value of the limiter. Therefore, after limiting the frequency demodulator does not receive a high-frequency signal component. Consequently, the demodulator generates a low-frequency signal, i.e. a television receiver will reproduce a black picture content. This means that signal inversion has occurred.